t as a result, although it seems to need to assume that each measurement is an instantaneous ideal measurement. The decay of the system can be slowed down or even prevented. This is called quantum Zeno eect. The problem was discussed in Beskow-Nilsson [BN], Misra-Sudarshan [MS]. Zeno is a Greek philosopher who said something like “A flying arrow does not fly”. The aim of this talk is to present the following product formula on quantum Zeno dynamics. This note is mainly based on the joint work with P.Exner [EI]. Theorem. Let H be a nonnegative selfadjoint operator in a separable Hilbert space $ \mathcal{H}$
The construction of unitary operator bases in a finite-dimensional Hilbert space is reviewed through a nonstandard approach combining angular momentum theory and representation theory of SU (2). A single formula for the bases is obtained from a polar decomposition of SU (2) and is analyzed in terms of cyclic groups, quadratic Fourier transforms, Hadamard matrices and generalized Gauss sums. Weyl pairs, generalized Pauli operators and their application to the unitary group and the Pauli group naturally arise in this approach.
Two sample constructions of all the Hilbert spaces for a given operator H of an observable
An elementary set of non-Hermitian N by N matrices H(N)(λ)=[H(N)(λ)]† with real spectra is considered, assuming that each of these matrices represents a selfadjoint quantum Hamiltonian in an {\it ad hoc} Hilbert space of states H(physical). The problem of an explicit specification of all of these spaces (i.e., in essence, of all of the eligible {\it ad hoc} inner products and metric operators Θ) is addressed. The problem is shown exactly solvable and, for every size N=2,4,... and parameter λ∈(−1,1) in matrix H(N)(λ), the complete N−parametric set of metrics Θα1,α2,...,αN(N)(λ) is recurrently defined by closed formula.